It's really difficult to say for certain, but it
might be a bug. Ideally, it'd be good to see if you can find a way to reliably reproduce the problem. So, is there a particular process where this occurs, or similar. Or, even better, see if it's reproducible reliably from the demo site at
https://demo7.dspace.org. Obviously, any developer would need to find a way to reproduce the same issue locally... as that would provide the clues needed to determine why it isn't working properly.
If you find that it's a really random issue (not easy to reliably reproduce) then it might be best to look for underlying errors using the Troubleshooting guide:
https://wiki.lyrasis.org/display/DSPACE/Troubleshoot+an+error#Troubleshootanerror-DSpace7.x(orabove) Random behavior could mean there's some error behind the scenes, which could either be a bug or a configuration issue or similar.